All the great teachers of Yoga have emphasised the importance of Yoga-Postures or Asanas. In the classical textbooks there are detailed descriptions of the significance, qualities, merits as well as the correct methods for the performance of Asanas. They assume new significance in modern times.
The western system of physical exercises, aimed at developing the bulk and the power of the muscle-masses, is the most commonly used system all over the world. This system is primarily, if not entirely, based on processes generating great tensions in the muscles. There is no corresponding relaxation of any group of muscles. The exertion in performing these exercises is harmful to the osteo-articular surfaces which are utilised in these movements. Consequently, a pent-up tension in the motor organs of the body is sometimes accompanied by varying degrees of organic injury. Chronic arthritic and arthromyalgic incapacity, which cripples the able-bodied, can to some extent be traced to this single cause.
The Yogic Asanas, on the other hand, do not aim especially at developing beautiful contours or extraordinary physical power. They aim at a homogeneously integrated system of neuro-muscular movements in which contraction of the muscles is always consciously followed by their relaxation or the relaxation of some other muscle-masses. At every step, a mental association is established with the physical actions, so that the unfathomable reserves and powers of the mind are harnessed for achieving a perfect physical culture of the entire body.